A mechanism for the biochemical regulation of the growth of the corneal epithelium is proposed. It is suggested that an increase in the intracellular level of cyclic AMP reduces mitotic activity and cell locomotion, and perhaps enhances the production of basement membrane and the adhesion of cells to the stroma. An increase in the intracellular level of cyclic GMP should have the opposite effects. Humoral factors such as catecholamines and prostaglandins would, therefore, discourage cell regrowth, and cholinergic agents should encourage it. The effects of these first and second messengers and their inhibitors on the regrowth of epithelium will be studied in vitro and in vivo. Growth will be assessed by counting cells in culture, measuring re-epithelialization of the stromal surface, examination of cellular structure and ultrastructure and by the incorporation of labelled precursors into proteins and nuclei acids.